Abstract. Hydromorphodynamic models are powerful tools for
predicting the potential mobilization and transport of sediment in river
ecosystems. Recent studies have shown that they are able to predict
suspended sediment matter concentration in small river systems
satisfactorily. However, hydro-sedimentary modelling exercises often neglect
suspended sediment properties (e.g. sediment densities and grain-size
distribution), which are known to directly control sediment dynamics in the
water column during flood events. The main objective of this study is to
assess whether a better representation of such properties leads to an
improved performance in the model. The modelling approach utilizes a fully
coupled hydromorphodynamic model based on TELEMAC-3D (v7p1) and an enhanced
version of the sediment transport module SISYPHE (based on v7p1), which
allows for a refined sediment representation (i.e. 10-class sediment
mixtures instead of 2-class mixtures and distributed sediment density instead of
uniform). The proposed developments of the SISYPHE model enable us to
evaluate and discuss the added value of sediment representation refinement
for improving sediment transport and riverbed evolution predictions. To this
end, we used several model set-ups to evaluate the influence of sediment
grain-size distribution, sediment density, and suspended sediment
concentration at the upstream boundary on model predictions. As a test case,
we simulated a flood event in a small-scale river, the Orne river in
north-eastern France. Depending on the model set-up, the results show
substantial discrepancies in terms of simulated bathymetry evolutions.
Moreover, the model based on an enhanced configuration of the sediment
grain-size distribution (10 classes of particle sizes) and with distinct
densities per class outperforms the standard SISYPHE configuration, with
only two sediment grain-size classes, in terms of simulated suspended
sediment concentration.
Sediment transport modelling in riverine environments: on the importance of
grain-size distribution, sediment density and boundary conditions
